Add compose per-pageload UKM metrics

This creates an object which records UKM when it is destroyed. This
allows us to record when a tab is closed directly. Otherwise, we record
when the PrimaryPageChanged event is called.

See go/ukm-collection-chrome-compose for review and approval details.

Bug: 319478359
Change-Id: I9e9a269471a4999bceeda1d81c46e2f0bf3848b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5208315
Reviewed-by: Peter Williamson <petewil@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Justin DeWitt <dewittj@chromium.org>
Auto-Submit: Justin DeWitt <dewittj@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1249087}